To speak of this subject you must... explain the nature of the resistance of the air, in the second the anatomy of the bird and its wings, in the third the method of working the wings in their various movements, in the fourth the power of the wings and the tail when the wings are not being moved and when the wind is favourable to serve as guide in various movements.

Those who become enamoured of the art, without having previously applied to the diligent study of the scientific part of it, may be compared to mariners who put to the sea in a ship without rudder or compass and therefore cannot be certain of arriving at the wished for port.

The knowledge of the past times and of the places of the earth is both an ornament and nutriment to the human mind.

You should look at certain walls stained with damp, or at stones of uneven color. If you have to invent some backgrounds you will be able to see in these the likeness of divine landscapes, adorned with mountains, ruins, rocks, woods, great plains, hills and valleys in great variety; and expressions of faces and clothes and an infinity of things which you will be able to reduce to their complete and proper forms. In such walls the same thing happens as in the sound of bells, in whose stroke you may find every named word which you can imagine.

Learning acquired in youth arrests the evil of old age; and if you understand that old age has wisdom for its food, you will so conduct yourself in youth that your old age will not lack for nourishment.

The color of the object illuminated partakes of the color of that which illuminates it.

The wisest and noblest teacher is nature itself.